Blood thrombus, embolus or clots may occur in a person's vasculature system. Sometimes such clots are harmlessly dissolved in the blood stream. Other times, however, such clots may lodge in a blood vessel, where they can partially or completely occlude the flow of blood, referred to as an ischemic event. If the partially or completely occluded vessel feeds blood to sensitive tissue such as, the brain, lungs or heart, serious tissue damage may result. Such ischemic events may also be exacerbated by atherosclerosis, a vascular disease that causes the vessels to become narrowed and/or tortuous. The narrowing and/or increased tortuousness of the blood vessels may, in certain circumstances, lead to the formation of atherosclerotic plaque that can cause further complications.
Known embolectomy devices may be used in a variety of applications to remove blood clots or other foreign bodies from blood vessels. Such devices includes ones cylindrical scaffold embolectomy devices, such those illustrated and described in U.S. Pat. No. 8,529,596 to Grandfield, which is fully incorporated herein by reference.
FIGS. 1A-B illustrate an exemplary prior art embolectomy device 12 that is manufactured and sold by the Neurovascular Intervention Division of Stryker Corporation (http://www.stryker.com/en-us/products/NeurovascularIntervention/index.htm). FIG. 1A shows the embolectomy device 12 in a two-dimensional plane view, and FIG. 1B shows the device 12 a three-dimensional expanded tubular configuration. The embolectomy device 12 is composed of shape memory, self-expandable and biocompatible materials, such as Nitinol. The embolectomy device 12 is preferably manufactured by laser cutting a tube or a sheet of shape memory material. The embolectomy device 12 is coupled to an elongate flexible wire 40 that extends proximally from device 12; the wire 40 is configured to push and pull the embolectomy device 12 through sheaths and/or catheters into a target site in a blood vessel.
As shown in FIG. 1A, the embolectomy device 12 includes a includes a proximal end portion 14, a main body portion 16 and a distal end portion 18, the main body portion including a plurality of longitudinal undulating elements 24 (e.g., wires, struts) with adjacent undulating elements being out-of-phase with one another and connected in a manner to form a plurality of diagonally disposed cell structures 26 extending between the respective proximal and distal end portions of the device. The cell structures 26 in the main body portion 16 and distal end portion 18 of the embolectomy device 12 extend continuously and circumferentially around a longitudinal axis 30 of the device 12 (FIGS. 1A-B).
In particular, the cell structures 26 in the proximal end portion 14 extend less than circumferentially around the longitudinal axis 30 of the device 12. The dimensional and material characteristics of the cell structures 26 of the main body portion 16 are selected to produce sufficient radial force (e.g., radial force per unit length of between 0.005 N/mm to 0.050 N/mm, preferable between 0.030 N/mm to 0.050 N/mm) and contact interaction to cause the cell structures 26, and/or the elements 24, to engage with an embolic obstruction residing in the vasculature in a manner that permits partial or full removal of the embolic obstruction from the patient. As best seen in FIG. 1B, the embolectomy device 12 has an overall length L1 of about 32 millimeters with the main body portion 16 length L2 measuring about 20 millimeters. Usually, the length of the main body portion 16 is generally between about 2.5 to about 3.5 times greater than the length of the proximal end portion 14.
FIG. 2 illustrates the embolectomy device 12 of FIGS. 1A-B disposed in a target site of a tortuous vascular anatomy of a patient capturing an embolic obstruction or clot 75. In an unexpanded or radially compressed configuration (not shown), such as when the embolectomy device 12 is disposed within a delivery catheter 80, the embolectomy device 12 has an unexpanded outer diameter (UOD) between 0.4 to 0.7 millimeters. In a radially expanded configuration (FIGS. 1B-2), the embolectomy device 12 has an expanded outer diameter (EOD) between 2.5 to 5.0 millimeters. The embolectomy device 12 produces sufficient radial force and contact interaction to cause the strut elements 24 and/or cell structures 26 to engage/snare/encapsulate/capture/pinch and/or entrap the embolic obstruction 75 disposed within the blood vessel 70, allowing removal of the embolic obstruction 75 from the patient. The diameter of the main body portion 16 in a fully expanded configuration is about 4.0 millimeters with the cell pattern, elements 24 dimensions and material being selected to produce a radial force of between 0.040 N/mm to 0.050 N/mm when the diameter of the main body portion is reduced to between 1.0 millimeters to 1.5 millimeters. The cell pattern 26, strut dimensions 24 and material(s) are selected to produce a radial force of between 0.010 N/mm to 0.020 N/mm when the diameter of the main body portion 16 is reduced to 3.0 millimeters. Having a strut thickness to width ratio of greater than one promotes integration of the strut elements 24 into the embolic obstruction 75.
Regardless of the technique used to manufacture the embolectomy device 12, the manner in which the strut elements 24 interconnect determines the device's longitudinal and radial rigidity and flexibility. Radial rigidity is needed to provide the radial force needed to engage the clot or embolic obstruction 75, but radial flexibility is needed to facilitate radial compression of the device 12 for delivery into a target site. Longitudinal rigidity is needed to pull an engaged clot or embolic obstruction 75 from the blood vessel 70, but longitudinal flexibility is needed to facilitate delivery of the device 12 (e.g., through tortuous vasculature). Embolectomy device 12 patterns are typically designed to maintain an optimal balance between longitudinal and radial rigidity and flexibility for the device 12. However, in certain applications, after deployment of the device 12 into the blood vessel 70, and once the embolectomy device 12 is subjected to tension/force for retraction or withdrawal, the device 12, particularly, the main body portion 16, tends to stretch creating a smaller profile or outer diameter (OD), similar to the unexpanded outer diameter (UOD) described above (e.g., between 0.4 to 0.7 millimeters).
FIG. 3A illustrates the embolectomy device 12 of FIGS. 1A-B and 2, disposed in a blood vessel 70 distally located from the catheter 80 and having a smaller profile/OD. The stretching of the device 12 and smaller profile/OD may cause the device 12 to be withdrawn past the embolic obstruction 75 without engaging or capturing the obstruction 75, as shown in FIGS. 3A and 3D. FIG. 3B-D are cross-sectional views of the blood vessel 70 having a lumen 72 with the embolic obstruction 75 therein. In an embolectomy procedure for removing the embolic obstruction 75 from the blood vessel lumen 72, the delivery catheter 80 is advanced through the lumen 72, until the distal portion of the catheter 80 is disposed in a target site adjacent to the obstruction 75, with the radially compressed embolectomy device 12 disposed within the catheter 80, as shown in FIG. 3C. The embolectomy device 12 is then pushed distally relative to the catheter 80, or the catheter 80 is withdrawn proximally relative to the embolectomy device 12 (or some of each), in order to deploy the device 12 out of the catheter 80 and into the blood vessel lumen 72, allowing the no-longer radially constrained embolectomy device 12 to radially expand within the blood vessel lumen 72 in order to engage, ensnare and capture the obstruction 75.
However, in certain applications (e.g., hard/dense embolic obstruction 75) the radial expansion force 33 of embolectomy device 12 is not sufficient to overcome the hardness and resistive force 36 of the embolic obstruction 75 to allow the struts of device 12 to penetrate into and integrate with the clot 75, causing the device 12 to instead take the path of least resistance by extending around the obstruction 75, as shown in FIG. 3D. The undesirable elongated profile/OD of the device 12 when extending around the obstruction 75 tends to pass the embolic obstruction 75 without engaging, ensnaring or capturing the obstruction 75 when the device 12 is withdrawn.
Accordingly, there is a need to prevent undesirable stretching, elongation and/or reduction of the profile/OD of embolectomy devices when subjected to tension after deployment within a blood vessel, while also allowing for a desired reduction of the profile/OD when the device is re-sheathed for repositioning and/or withdrawal.